The present invention relates to polyorganosiloxane compositions, particularly to polyorganosiloxane compositions which are stable under a sealed condition but cure to an elastomer at room temperature through contact with moisture contained in air.
Polyorganosiloxane compositions which cure to an elastomer at room temperature may be employed in a variety of uses. Generally, these polyorganosiloxanes are of the one-component type wherein a curing reaction is effected through contact with the moisture contained in air. The uses for such polyorganosiloxanes include elastomeric adhesives, coating materials in the electric and electronic industries and also as a sealing material for buildings, etc. One-component polyorganosiloxanes do not require troublesome procedures before using, for example, weighing out the main component, crosslinking agent and catalyst as well as mixing thereof, whereby the mistakes are avoided which may be caused during such procedures.
Room temperature curable polyorganosiloxane compositions generally comprise a polydiorganosiloxane having terminal silanol groups which is mixed with a crosslinking agent etc. having an average of more than two hydrolytic groups in a molecule. Upon cure, the compositions release acetic acid, long chain carboxylic acids, organic amines, amides, organic hydroxylamines, oxime compounds, alcohols, acetone or the like depending on the kind of crosslinking agent.
Among these compositions, those which release acetic acid have excellent adhesiveness and curing property. However, they are disadvantageous in that they emit irritating odor, requiring countermeasures for protecting environmental health. Further, in the case where the substrate to be coated is metal, they rust the metal, requiring countermeasures for preventing rusting, etc. Those compositions which release long-chain carboxylic acids have no problem of developing irritating odor but in such compositions it has been difficult to prevent rusting of metals, particularly after the metals have been immersed in water. Similarly, those which release amines have disadvantages in the odor and toxicity of the amines which are released therefrom and those which release hydroxylamines, oximes or amides have disadvantages that they rust metal easily, especially copper and its alloys. Further, while those which release acetone cure rapidly and are free from corrosiveness, they have disadvantages in that synthesis of the crosslinking agent is difficult and the uncured composition yellows upon storage.
In contrast to the above compositions, those which release alcohols have advantages that alkoxysilanes as cross-linking agents are available at low cost. Also, they are free from odor and corrosiveness since by-products released therefrom are easily volatilized alcohols such as methanol or ethanol. On the other hand, however, they have disadvantages that they cure slowly and that they have poor storage stability. Where water impurities are present, the base polymer is cleaved by the alcohol released as a result of hydrolysis of the crosslinking agent.
Especially in electric and electronic industries, room temperature curing polyorgano-siloxane compositions are frequently cured in a state in contact with copper series metals to form rubber-like elastomers and are used as adhesives, coating materials, etc. Accordingly, oxime releasing compositions, acetone releasing compositions and alcohol releasing compositions have conventionally been used, but improvement of the disadvantages as mentioned above have been desired.
It has recently been found that a one-component type room temperature curing polyorganosiloxane composition comprising a polyorganosiloxane having terminal silicon atoms bonded to alkoxy groups, an alkoxysilane, a curing catalyst and an alcohol scavenger, has excellent storage stability and cures rapidly (refer to Japanese Provisional Patent Publication Nos. 59-500219 (1984) and 58-501040 (1983)). It has also been found that if a compound containing silicon-nitrogen bonds is used as the alcohol scavenger, a nonvolatile nitrogen containing compound is formed through reaction with an alcohol and the resulting composition does not exhibit corrosiveness to copper series metals.
While such room temperature curable polyorganosiloxane compositions which cure rapidly and do not rust copper series metals are useful as adhesives or as coating materials in the electric and electronic industries, they still exhibit certain problems. The compound containing the silicon-nitrogen bond as an alcohol scavenger is hydrolyzed and the hydrolyzate bleeds to the surface of the cured rubber and resinified, which gives cracks on the surface leading sometimes to low physical properties or low durability of the cured rubber.
The present inventors have previously found that a compound containing a polyoxyalkylene chain in a molecule is effectively used to prevent such resinification and have filed a patent application therefor (Japanese Patent Application No. 58-125649 (1983); Japanese Provisional Patent Publication No. 60-18544 (1985)).
However, a composition obtained according to the above method does not adhere sufficiently to certain plastic substrates to be coated. Namely, it exhibits poor adhesiveness to polycarbonate substrates. Also, there may sometimes not be obtained satisfactory results in terms of adhesiveness to acrylic resin substrates depending on the conditions under which they are employed. For such reasons, the above composition has not been appropriate for uses wherein polycarbonate or acrylic resin is used in spite of its many advantages namely, it is free from corrosiveness to copper series metals, it cures in a relatively short time at room temperature and also is free from bleeding.